The possibility of using phase change materials (PCMs) in nonvolatile memory cells has recently gained momentum as more is learned about these materials and their integration into integrated circuits. When incorporated into a memory cell, these materials may be toggled between higher and lower electrical resistance states by applying a pulse of electrical current (“switching current pulse”) to the memory cell. Subsequently, after writing to a memory cell in this way, the electrical resistance state of the given memory cell may be determined (i.e., read) by applying a low magnitude sensing voltage to the material in order to determine its electrical resistance state. Notably, in some designs, a PCM-based memory cell may even be able to simultaneously store more than one bit of information.
Currently, binary and ternary chalcogenide alloys such as doped SbTe and Ge2Sb2Te5 (GST) are showing the greatest promise for use in practical PCM-based memory cells. A. Pirovano et al., “Electronic Switching in Phase-Change Memories,” IEEE Transactions on Electron Devices, Vol. 51, No. 3, March 2004, for example, describes such a use of chalcogenides and is incorporated herein by reference. However, the switching of a PCM-based memory cell requires that the switching current pulse produce enough heat in the PCM to cause at least some portion of the PCM to reproducibly change electrical resistance state. The required temperature, for example, may be as high as 650 degrees Celsius. If the memory cell is not properly designed, the magnitude of the switching current pulse necessary to create these required temperatures may easily exceed that which can be tolerated by modern integrated circuits.
For this reason, a thin film memory cell is an attractive solution for PCM-based memory cells. In such a memory cell, the switching current is forced along a thin film of PCM. As a result, the magnitude of the switching current may be tuned by adjusting the thickness of the PCM layer as well as its width and the length through which the switching current must pass. Nevertheless, despite the apparent advantages of such a design, precise control of these dimensional parameters remains challenging from a processing standpoint. Accordingly, there remains a need for an easily manufactured thin film PCM-based memory cell that allows precise tuning of the switching current pulse magnitude.